The present invention is a method for determining the efficiency of a catalytic converter in an internal combustion engine on a vehicle equipped with a computerized closed-loop control system. The efficiency of the catalytic converter is measured by the reduction of the levels of carbon monoxide and hydrocarbons in the exhaust stream of the engine. Previous methods for determining the efficiency of a catalytic converter in an automotive exhaust system are not readily adaptable to the modern internal combustion engine. The present invention is particularly applicable to the field of automotive testing and repair where environmental and consumer protection legislation has been enacted which mandates the testing of catalytic converters.
Since 1967, legislative and market pressures have caused automobile engines and their associated control systems to become increasingly complicated. To meet the combined effects of stringent pollution controls and Corporate Average Fuel Economy (CAFE) requirements, automobile manufacturers have incorporated closed-loop controls using sensors, actuators and on-board computers. The closed-loop systems closely monitor and control the fuel mixture burned by the engine and are essential in permitting manufacturers to satisfy certification requirements mandated by the Environmental Protection Agency (EPA). However, repair of these closed-loop control systems has proved to be extremely difficult when one or more of the components fails or becomes marginally functional. As additional legislation is enacted, more and more vehicles will be equipped with complex computerized systems to monitor fuel consumption and emission levels.
Prior to 1967, a tune-up involved locating and replacing malfunctioning components which were either carburetor or ignition related. Failure modes were obvious and replacement or rebuilding of the components was the preferred corrective measure. By the middle 1970's, Inspection and Maintenance (I&M) programs had been introduced in a number of states such as California, New Jersey, New York and Arizona. I&M programs require that some method of testing be conducted to verify compliance with state mandated emission limits. Exhaust analyzers measuring levels of carbon monoxide and hydrocarbons were introduced to facilitate emission levels testing and to isolate carburetor from ignition problems. Carbon monoxide analysis is primarily used to set carburetion, while hydrocarbon analysis is used primarily to isolate ignition and timing problems.
The addition of the catalytic converter on 1975 and later model year vehicles increased the complexity of the inspection, maintenance and repair process. The catalytic converter masks the emission levels of carbon monoxide and hydrocarbons used by the technician to identify engine and emission system failures. The high signatures of carbon monoxide and hydrocarbons the technician previously relied on to isolate failed or malfunctioning components are effectively eliminated by a properly operating converter. Thus, although the catalytic converter is a powerful device for reducing emission levels, it makes adjustment of engine and exhaust system components on vehicles in need of repair or which have failed emission levels tests more difficult.
The development of analyzing equipment to measure oxygen levels and the incorporation of methods of intermittent misfire detection has eliminated much of the uncertainty encountered when adjusting carburetion and timing to tune a vehicle or to pass emission tests. An apparatus employing oxygen measurement and intermittent misfire detection is described in U.S. Pat. No. 4,030,349 entitled "IMPROVED ENGINE ANALYSIS APPARATUS" filed in the name of John D. Blanke et al., and U.S. Pat. No. 4,031,747 entitled "MISFIRE MONITOR FOR ENGINE ANALYSIS HAVING AUTOMATIC RESCALING" filed in the name of John D. Blanke. The '349 and '747 patents are incorporated by reference into the present disclosure in their entireties.
Catalytic converters are standard equipment on vehicles manufactured after 1975 and have become the major weapon in the reduction of emission levels. Unfortunately, however, existing catalytic converters cease to be effective when the catalyst is exhausted or becomes poisoned. Further, when the catalytic converter is operating effectively and reducing emission levels, it is simultaneously reducing the accuracy of testing and repair methods which rely on the same emission levels to evaluate the operation and integrity of engine and exhaust system components. Thus, while the converter solves one problem it creates another.
The technology of controlling emission levels remained relatively unchanged from 1975 until the 1980 model year. However in 1980, computerized closed-loop control systems were introduced to monitor fuel consumption and reduce emission levels on vehicles destined for the state of California. These closed-loop systems were designed to meet newly legislated fuel economy standards while satisfying federal and state mandated emission limits. Within a short time, computerized closed-loop control systems became standard equipment on most new vehicles. Today, almost all vehicles sold in the United States contain some form of computerized fuel management and emission levels control technology.
An apparatus and procedure for determining the efficiency of an automotive exhaust system including a catalytic converter for removing unburned carbon monoxide and hydrocarbons from the exhaust stream is disclosed in U.S. Pat. No. 4,116,053 entitled "THERMAL REACTOR/CATALYTIC CONVERTER EFFICIENCY DETERMINATION METHOD" filed in the name of John D. Blanke. However, the method described in the '053 patent is not readily adapted to modern vehicles equipped with computerized closed-loop control systems. In fact, in order to practice the '053 invention on a modern vehicle, the technician must disable the portion of the closed-loop control system which monitors the fuel mixture. If not disabled, the closed-loop control system automatically maintains the fuel mixture at 14.7:1 (air to fuel ratio) while the operator manually attempts to adjust the fuel mixture to create lean and rich operating conditions as taught by the '053 patent. Disabling the closed-loop control system causes the engine to run full rich or full lean depending on the design of the mixture-control device. To offset the effects of disabling the closed-loop control system on a carbureted engine, the idle mixture screws must be reset. The procedure to adjust the idle mixture screws entails removing the carburetor, drilling holes into it, driving out the anti-tamper caps covering the screws, reinstalling the carburetor and manually adjusting the screws as needed to induce a lean operating condition. Worse still, the technician must restore the engine to its original operating condition after completing the analysis of the exhaust system. More often than not, the technician can end up performing a complete tune-up on the engine after completing the test.
The method disclosed by the '053 patent is also not readily adapted to vehicles equipped with fuel-injection systems. For the same reason, to practice the '053 invention on a engine in which the fuel is directed to the cylinders by fuel injectors, the technician must physically alter the injector settings or replace the fuel injectors to induce a lean operating condition. As in the case of the carbureted vehicle, the technician can end up performing a complete tune-up on the engine.
Another problem is that the method disclosed by the '053 patent has proved to be extremely hazardous to the untrained or careless technician. In order to induce a rich operating condition in a carbureted engine, the '053 patent instructs the technician to inject propane into the air cleaner inlet or carburetor throat. Although the '053 patent suggests removal of the air cleaner filter and assembly before injecting the propane, technicians, in an attempt to save time and effort, routinely do not. As a result, propane is spilled onto the air cleaner filter and housing and the likelihood of explosion is greatly increased.
The '053 patent also instructs that any method for determining the efficiency of an exhaust system including a catalytic converter must be convenient, accurate and rapid to be of practical value. Components of the engine and exhaust system are typically hot when presented to the technician and testing requires the engine to be run continuously during the procedure. Fine adjustments to the idle mixture screws on carbureted engines and to the metering settings on fuel-injected engines are difficult and tedious to make as well as to restore. Thus, it is evident that any method of testing which requires extensive handling and modification of the engine and exhaust system components is inconvenient, imprecise and time-consuming.
Accordingly, it is an object of the present invention to provide a feasible method for determining the efficiency of a catalytic converter in an internal combustion engine that includes a computerized closed-loop control system.
Another object of the invention is to provide a method for determining the efficiency of an exhaust system which is readily adapted to vehicles in which the engine is either carbureted or fuel-injected.
Another object of the invention is to provide a method for determining the efficiency of a catalytic converter which does not require procedures which are inconvenient, inaccurate or time-consuming.